Animal findings demonstrate that isolation from mother, decreased skin stimulation, and withholding of breastmilk have biochemical and permanent brain consequences. Correlating these findings with human behavioral research suggests which events lead to chronic stress and its permanent consequences:

• allowing a child to "cry it out" without parental attention and affection
• not feeding the child when hungry
• not offering comfort when the child is disturbed or distressed
• limiting body contact during feeding, throughout the day, and during stressful parts of the night
• low levels of human attention, stimulation, "conversation," and play

When these occur regularly, they can lead to early chronic releases of high levels of stress hormones, as well as low expression of favorable hormones, as previously discussed. All these practices have been promoted during the last century in the form of scheduled feedings, "don't spoil the child," bottle feedings, which lead to propped bottles, and physical separation during the day and night.

While it is evident that genetic makeup and life experiences influence behavior, it has been demonstrated that experiences during infancy have the strongest and most persistent effect on adult hormone regulation, stress responses, and behavior.⁵ Research has demonstrated that high levels of early physical contact and maternal responsiveness can even mitigate genetic predisposition for more extreme stress reactions.⁶

Biological psychology researcher Megan Gunnar and her colleagues did infant studies that confirmed animal research findings. In their work, infants three months of age who received consistent responsive care produced less cortisol. Also, eighteen-month-olds classified as insecurely attached (who had received lower levels of responsiveness) revealed elevated levels of stress hormone.⁷ These same children at age two continued to show elevated levels of cortisol and appeared more fearful and inhibited. Again, these children were those who had been classified as having lower levels of maternal responsiveness.⁸ Other investigations have confirmed these findings.⁹ Dr. Gunnar reports that the level of stress experienced in infancy permanently shapes the stress responses in the brain, which then affect memory, attention, and emotion.¹⁰

The HPA (hypothalamic–pituitary–adrenocortical) axis, a relationship between specific brain organs and the adrenal glands, is the chief regulator of stress reactions. While several hormones direct stress reactions, often in concert with each other and with some playing more than one role, cortisol is probably the most typical of the stress hormones. It is the subject of many recent reports. During stress, stress hormones are released under control of the HPA axis to help the body cope. Cortisol can elevate the blood pressure and the heart rate, increase blood sugar, and interrupt digestive and kidney functions.

Norepinephrine responses and cortisol responses are connected. Both are released in reaction to excitement, exercise, and stress. Both cause increased heart rate, blood sugar, and brain activity. I have discussed how surges of norepinephrine during affection and play can promote learning in infants (you may remember how you occasionally learned better under the stress and excitement of last-minute studying), as well as bonding (since bonding occurs in children and adults when they share exciting activity). However, chronic exposure to "negative" stress causes chronic elevations of cortisol, instead of surges that have a positive effect. Chronically elevated cortisol in infants and the hormonal and functional adjustments that go along with it are shown to be associated with permanent brain changes that lead to elevated responses to stress throughout life, such as higher blood pressure and heart rate.¹¹ This elevated response begins quite early. Even infants regularly exposed to stress already demonstrate higher cortisol releases and more sustained elevations of cortisol in response to stressful situations.¹²

Occasional surges of cortisol throughout the day can be beneficial, but continuously elevated stress hormone levels in infancy from a stressful environment are associated with permanent "negative" effects on brain development. Some evolutionary theories even go so far as to suggest that the heightened stress responses that apparently lead to aggressive behavior and early puberty serve a purpose, aiding survival of the species during drought, war, or other hardships.

Studies have shown that infants who receive frequent physical affection have lower overall cortisol levels,¹³ while psychological attachment studies reveal higher levels in insecurely attached children.^14,15 Women who breastfeed also produce significantly less stress hormone than those who bottle-feed.¹⁶

Without regular closeness to a caregiver, an infant not only suffers from elevated stress hormones, but also receives less benefit from oxytocin surges and other positive biochemical influences. The biochemical environment imposed on an infant's brain during critical development stages affects the anatomy and functioning of the brain permanently.¹⁷ A poor biochemical environment results in less desirable emotional, behavioral, and intellectual abilities for the rest of a child's life.

As previously described, a brain developed in a stressful environment overreacts to stressful events and controls stress hormones poorly throughout life. Levels of cortisol and other stress hormones are regularly elevated in these individuals. As adults they may demonstrate "type-A" behavior, which is associated with a high risk of heart disease and adult-onset diabetes. Interestingly, one psychiatrist found that the poor health consequences for adults who received restricted mothering during childhood – high blood pressure and high levels of cortisol – closely resemble those in adults who lost a parent as a child.¹⁸ The effects, however, go way beyond one's blood pressure and ability to deal with stress.

The hippocampus, a structure important in learning and memory, is one brain site where development is affected by stress and bonding hormone levels. The level of the stress hormones circulating in an infant affects the number and types of receptors here.¹⁹ It has also been demonstrated that nerve cells in the hippocampus are destroyed as a result of chronic stress and elevated stress hormone levels, producing intellectual deficits as a consequence.²⁰ Memory and spatial learning deficits have been demonstrated in rats that suffered prolonged stress in infancy.²¹ Similarly, children with the lowest scores on mental and motor ability tests have been shown to be the ones with the highest cortisol levels in their blood.²²

Premature development of puberty has also been associated with significantly higher levels of cortisol and other stress indicators.²³ This study additionally reports that these children have more depression, more behavior problems, and lower intelligence scores. Here again, the laboratory studies fully confirm psychological attachment studies. Furthermore, premature puberty increases one's risk of developing cancer.

In individuals who suffer from anxiety disorders, anorexia nervosa, and depression, excess production of cortisol is a very consistent finding.²⁴ Oversecretion of stress hormones has also recently been implicated in obesity, Alzheimer's disease,²⁵ and accelerated aging symptoms.²⁶ Animal studies have demonstrated decreased immune system functioning in infants subjected to the stresses of prolonged separation from mother,^27,28 which coincides with the increased incidence of illness shown in less-attached children.

Much has been written about the first moments after a child is born. The infant, (if not entirely intoxicated by drugs used in labor), has been primed by hormones during the birth process to be born wide awake and alert for a short while. During this time the initial imprinting takes place. Already familiar with the voices of his parents, the baby, who can distinguish faces from other objects and body parts, gazes intently into the eyes of his parents, as if to record their images for life. He recognizes the odor of the amniotic fluid, which is chiefly his own, but is also that of his mother. His important early programming guides his mouth to seek and find a new physical method of maternal nourishment, and he is immediately attracted to the specific odor of the nursing vessels that will now replace his umbilical cord. The newborn, barely able to maintain his body temperature, finds comfort and ideal temperature regulation in contact with mom's warm body. Having known only the firm secure confinement of his womb, he feels comfortable against a warm body or in secure arms, and he will cry loudly, uncomfortable and anxious, if left to flail on a cold, hard surface. With his first taste of concentrated nutrition and immunity-providing colostrum, and hearing the familiar beating and gurgling sounds of mother's body, he soon falls into a peaceful sleep – even his heartbeat and breathing are regulated by mother's rhythms. As he sleeps, his first breaths and tastes of his mother establish normal, healthy flora in his digestive tract, providing defense against the less friendly microbes all around him.

Although all is not lost if an infant's life did not begin this way, this is the first chance for attachment and the first choice made regarding baby's health. There is a long life ahead for parents and child, and there are many directions a family can take. While a child is born seeded with specific potential (nature), the parenting style (nurture) will greatly influence the likelihood these latent abilities will come to fruition, much to the benefit or detriment of the child, family, and society.

Research on the biochemical factors influenced by child care methods demonstrates that with responsive parenting the body produces substances to help generate effective, loving, and lasting parents for an infant and infants who are strongly bonded to their parents. Over time these bonds mature into love and respect. Without a doubt these chemicals permanently organize an infant's brain toward positive behaviors and later development of strong, lasting attachments. However, the greatest lesson from these studies is that while nature has a very good plan, failure to follow it may lead to less desirable results. In other words, when parents heed instinctive desires to enjoy a great deal of closeness with their infants, by feeding them naturally and responding quickly to their needs and desires (which in the infant are truly one in the same), nature is designed to develop sensitive responsible adults. Withholding attention from an infant allows the vital chemical messengers to quickly diminish, and as a result, weak bonds are formed, and parenting becomes more arduous and less successful. At the same time, the infant manifests the effects of stress. Moreover, stress reactions and other behaviors in a child and the adult he will become are permanently altered in unfortunate ways. Aspects of the intellect and health may suffer as well.

The incredible, extensive, innate human system of hormonal rewards for consistent, close, and loving physical and social contact between parent and infant, and the just as incredible consequences, combined with the psychological research findings about attachment, provide overwhelming evidence for the intended plan for infant care, at least for me.

I once heard an older pediatrician say to a mother, strongly disapproving of the way her toddler clung to her and demanded that she hold him while his blood was drawn, "It all starts the first day you pick him up when he cries."